Certain polysaccharides purified from the surface of bacterial cells exhibit protective effects in vivo when tested in models of inflammation such as the formation of intraabdominal abscesses, intraabdominal sepsis, and post-surgical adhesions. U.S. Pat. Nos. 5,679,654 and 5,700,787; published international patent applications WO 96/07427, WO 00/59515, and WO 02/45708). When purified from whole capsule, certain polysaccharides derived from Bacteroides fragilis, Staphylococcus aureus, and Streptococcus pneumoniae have unique characteristics that set them apart from many polysaccharide antigens. These molecules are high molecular weight, helical, and zwitterionic in nature. Wang Y et al. (2000) Proc Natl Acad Sci USA 97:13478-81; Brubaker J O et al. (1999) J Immunol 162:2235-42; Tzianabos A O et al. (1995) Infect Immun 62:4881-6; Tzianabos A O et al. (1995) J Clin Invest 96:2727-31; Kalka-Moll W M et al. (2000) J Immunol 164:719-24; Tzianabos A O et al. (2000) J Biol Chem 275:6733-40.
Most bacterial polysaccharides are neutral or negatively charged and are considered to be T-cell-independent antigens. Abbas A K et al. (2003) Cellular and Molecular Immunology, Saunders, Philadelphia. It has been suggested, however, that the zwitterionic nature of these polysaccharides somehow involves them in interaction with CD4+ T cells. Tzianabos A O et al. (1993) Science 262:416-9; Tzianabos A O et al. (2001) Proc Natl Acad Sci USA 98:9365-70. That zwitterionic polysaccharides activate CD4+ T cells in vitro is supported by their reported ability to stimulate T-cell proliferation and the production of the cytokines IL-2, IFN-γ, and IL-10. In addition, it has been reported that the protective effect is adoptively transferred by polysaccharide-stimulated T cells in vivo. Published international patent application WO 00/59515; Kalka-Moll W M et al. (2000) J Immunol 164:719-24; Tzianabos A O et al. (2000) J Biol Chem 275:6733-8. It remains unclear, however, exactly how these molecules activate T cells or how they exert their protective effects.